Humankind has, since ancient times, lived close to the sea, rivers and lakes. The remains of ports, bridges and fishing installations are testimony of this close connection.

Ports

Countless ports around the world are of considerable age, some of them still function, others have been abandoned or even forgotten. However, their breakwaters, protections and related buildings can still give evidence of their size. Also, shipwrecks are often located around these ports.

Examples of submerged port structures can be found in:

• Hedeby, Germany, hosting remains of a Viking trading port destroyed in 1,050 A.D;
• Remains of the ancient Ports of Ostia near Rome and Portus Iulius in the Bay of Naples, Italy;
• The remains of a massive Byzantine port in Istanbul (Yenikapi) dating back to the 4th century A.D featuring the oldest settlement in the city, the earliest city wall and at least 22 shipwrecks, including the first Byzantine galley ever found;
• Well-preserved remains of a small Roman port in a bay on the island of Brioni, Croatia;
• The remains of the port of Caesarea, Israel, which was founded by King Herod in 22 B.C (now an underwater park for scuba divers);
• Remains of the Phoenician naval base of Carthage dating from 814 BC, near Tunis, Tunisia;
• The remains of the Phoenician port of Tyre, Lebanon.

Bridges and constructions

Remains of water-related structures and bridge can also be found in the bottom of rivers and lakes. For example:

• The oldest Bridge across the River Thames, England, dating from 1,400-1,300 B.C;
• A 120 m long wooden bridge over the River Shannon, Ireland, dating from 804 B.C;
• A marine fortification from the 18th century found in the bay of Tallinn, Estonia;
• A submerged bridge located at 49 m depth in Lake Murray, South Carolina, USA.

Fish traps and fences

Many ancient populations used to build fish traps, the remains of which survive today. They represent some of the oldest existing working technology. Fish traps are found in many forms. They range from artificial rock pools consisting of low stone walls built from beach stones, to complex arrangements of stone walls several hundred meters in length. Sometimes they are also built using timber stakes wrapped with plant material and are placed in the middle of a stream, in an estuary or near the coastline. The fish were usually herded into the impoundment area where they could be retrieved.

Remains of ancient fish traps as well as clam gardens can be found in or off:

• The South Western Cape coast, South Africa;
• Caernarvon Bay, N. Wales and Denmark (Stone Age fish traps);
• The Pacific Islands and Hawaii (where such ancient traps are considered holy);
• Canada (made by Indigenous tribes in approx. 7,500-3,500 BC);
• Australia (Aboriginal fish traps at Lake Condah and in the Darling River).

Technical instruments

Traces of the progress of navigation, humans skills and understanding of the universe have also been found on the bottom of the sea. The remains of complicated mechanisms that are found are rare objects, but even more remarkable:

• Several astrolabes have been found on shipwrecks. They are historical astronomical instruments used to locate and predict the positions of the sun, the moon and the stars. They may help to determine the local time given the local latitude;
• The mysterious Antikythera mechanism was found on a shipwreck discovered off the coast of Greece. It is considered to be the world’s oldest known analog computer, in the form of a complex scientific calculator created around 100 BC. The mechanism is supposed to have served to calculate astronomical positions and eclipses of the sun and moon.